U.S. patent application number 17/718493 was filed with the patent office on 2022-07-28 for topside distributed acoustic sensing interrogation of subsea wells with a single optical waveguide.
This patent application is currently assigned to Halliburton Energy Services, Inc.. The applicant listed for this patent is Halliburton Energy Services, Inc.. Invention is credited to Andreas Ellmauthaler, John L. Maida, Glenn Andrew Wilson.
Application Number | 20220236106 17/718493 |
Document ID | / |
Family ID | 1000006259830 |
Filed Date | 2022-07-28 |
United States Patent
Application |
20220236106 |
Kind Code |
A1 |
Ellmauthaler; Andreas ; et
al. |
July 28, 2022 |
Topside Distributed Acoustic Sensing Interrogation Of Subsea Wells
With A Single Optical Waveguide
Abstract
A distributed acoustic system (DAS) may comprise an interrogator
and an umbilical line attached at one end to the interrogator, a
downhole fiber attached to the umbilical line at the end opposite
the interrogator. The interrogator may further include a proximal
circulator, a distal circulator connected to the proximal
circulator by a first fiber optic cable, and a second fiber optic
cable connecting the proximal circulator and the distal
circulator.
Inventors: |
Ellmauthaler; Andreas;
(Houston, TX) ; Wilson; Glenn Andrew; (Houston,
TX) ; Maida; John L.; (Houston, TX) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Halliburton Energy Services, Inc. |
Houston |
TX |
US |
|
|
Assignee: |
Halliburton Energy Services,
Inc.
Houston
TX
|
Family ID: |
1000006259830 |
Appl. No.: |
17/718493 |
Filed: |
April 12, 2022 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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16806930 |
Mar 2, 2020 |
11326936 |
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17718493 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G02B 6/02076 20130101;
G01V 1/52 20130101; H04J 14/02 20130101; G01H 9/004 20130101; E21B
47/135 20200501; G01V 1/38 20130101 |
International
Class: |
G01H 9/00 20060101
G01H009/00; G01V 1/38 20060101 G01V001/38; G02B 6/02 20060101
G02B006/02; G01V 1/52 20060101 G01V001/52; E21B 47/135 20060101
E21B047/135 |
Claims
1. A distributed acoustic system (DAS) comprising: an interrogator;
an amplifier connected to the interrogator by a first fiber optic
cable; a pump laser connected to the amplifier by a second fiber
optic cable; and a downhole fiber connected to the amplifier.
2. The DAS of claim 1, further comprise a second amplifier.
3. The DAS of claim 2, further comprise a second pump laser
connected to the second amplifier by a third fiber optic cable.
4. The DAS of claim 3, further comprising a fourth fiber optic
cable that connects the amplifier to the second amplifier.
5. The DAS of claim 4, wherein the pump laser is a Raman Pump.
6. The DAS of claim 1, further comprising a proximal circulator and
a distal circulator disposed on the first fiber optic cable between
the interrogator and the amplifier.
7. The DAS of claim 6, further comprising an erbium doped fiber
amplifier (EDFA) disposed between the proximal circulator and the
distal circulator on a third fiber optic cable.
8. The DAS of claim 7, further comprising an optical shutter
disposed between the EDFA and the distal circulator on the third
fiber optic cable.
9. A distributed acoustic system (DAS) comprising: an interrogator;
a proximal circulator connected to the interrogator by a first
fiber optic cable; a distal circulator connected to the proximal
circulator by a second fiber optic cable; and a downhole fiber
connected to the distal circulator.
10. The DAS of claim 9, further comprising an amplifier disposed on
the second fiber optic cable between the proximal circulator and
the distal circulator.
11. The DAS of claim 10, further comprising a pump laser connected
to the amplifier by a third fiber optic cable.
12. The DAS of claim 11, further comprising a second amplifier
disposed on a fourth fiber optic cable that connects the proximal
circulator to the distal circulator.
13. The DAS of claim 12, a second pump laser connected to the
second amplifier by a fifth fiber optic cable.
14. The DAS of claim 13, wherein the pump laser and the second pump
laser are a Raman Pump.
15. A distributed acoustic system (DAS) comprising: an
interrogator; a proximal circulator connected to the interrogator
by a first fiber optic cable; a downhole fiber connected to the
proximal circulator; an amplifier disposed on the first fiber optic
cable; and a pump laser connected to the amplifier.
16. The DAS of claim 15, further comprising a second fiber optic
cable that connects the proximal circulator to the
interrogator.
17. The DAS of claim 16, further comprising a second amplifier
disposed on the second fiber optic cable.
18. The DAS of claim 17, wherein the second amplifier is connected
to the amplifier by a third fiber optic cable.
19. The DAS of claim 17, further comprising a second pump laser
connected to the second amplifier.
20. The DAS of claim 19, wherein the pump laser and the second pump
laser are a Raman Pump.
Description
BACKGROUND
[0001] Boreholes drilled into subterranean formations may enable
recovery of desirable fluids (e.g., hydrocarbons) using a number of
different techniques. A number of systems and techniques may be
employed in subterranean operations to determine borehole and/or
formation properties. For example, Distributed Acoustic Sensing
(DAS) along with a fiber optic system may be utilized together to
determine borehole and/or formation properties. Distributed fiber
optic sensing is a cost-effective method of obtaining real-time,
high-resolution, highly accurate temperature and strain (acoustic)
data along at least a portion of the wellbore. In examples,
discrete 8sensors, e.g., for sensing pressure and temperature, may
be deployed in conjunction with the fiber optic cable.
Additionally, distributed fiber optic sensing may eliminate
downhole electronic complexity by shifting all electro-optical
complexity to the surface within the interrogator unit. Fiber optic
cables may be permanently deployed in a wellbore via single- or
dual-trip completion strings, behind casing, on tubing, or in
pumped down installations; or temporally via coiled tubing,
slickline, or disposable cables.
[0002] Distributed sensing can be enabled by continuously sensing
along the length of the fiber, and effectively assigning discrete
measurements to a position along the length of the fiber via
optical time-domain reflectometry (OTDR). That is, knowing the
velocity of light in fiber, and by measuring the time it takes the
backscattered light to return to the detector inside the
interrogator, it is possible to assign a distance along the
fiber.
[0003] Distributed acoustic sensing has been practiced for dry-tree
wells, but has not been attempted in wet-tree (or subsea) wells, to
enable interventionless, time-lapse reservoir monitoring via
vertical seismic profiling (VSP), well integrity, flow assurance,
and sand control. A subsea operation may utilize optical
engineering solutions to compensate for losses accumulated through
long (.about.5 to 100 km) lengths of subsea transmission fiber, 10
km of in-well subsurface fiber, and multiple wet- and dry-mate
optical connectors, splices, and optical feedthrough systems
(OFS).
BRIEF DESCRIPTION OF THE DRAWINGS
[0004] For a detailed description of the preferred examples of the
disclosure, reference will now be made to the accompanying drawings
in which:
[0005] FIG. 1 illustrate an example of a well measurement system in
a subsea environment;
[0006] FIG. 2 illustrates an example of a DAS system;
[0007] FIG. 3 illustrate the example of a DAS system with lead
lines.
[0008] FIG. 4 illustrates a schematic of another example DAS
system;
[0009] FIG. 5 illustrates an example of a remote circulator
arrangement;
[0010] FIG. 6 illustrates a graph for determining time for a light
pulse to travel in a fiber optic cable;
[0011] FIG. 7 illustrates another graph for determining time for a
light pulse to travel in a fiber optic cable;
[0012] FIG. 8 illustrates an example of a remote circulator
arrangement;
[0013] FIG. 9 illustrates another graph for determining time for a
light pulse to travel in a fiber optic cable;
[0014] FIG. 10A illustrates a graph of sensing regions in the DAS
system;
[0015] FIG. 10B illustrates a graph with an active proximal
circulator using an optimized DAS sampling frequency of 12.5
kHz;
[0016] FIG. 10C illustrates a graph with a passive proximal
circulator using an optimized DAS sampling frequency of 12.5
kHz;
[0017] FIG. 11 illustrates a graph of optimized sampling
frequencies in the DAS system;
[0018] FIG. 12 illustrates an example of a workflow for optimizing
the sampling frequencies of the DAS system;
[0019] FIGS. 13-26 illustrate different examples of the DAS
system;
[0020] FIG. 27 illustrates an example of an interrogator in the DAS
system;
[0021] FIG. 28 illustrates a schematic of the interrogator with a
single photon detector;
[0022] FIG. 29 illustrates an examples of a single photon
detector;
[0023] FIG. 30 illustrates another example of the interrogator;
[0024] FIG. 31A-31D illustrates examples of a downhole fiber
deployed in a wellbore; and
[0025] FIG. 32 illustrates an example of the well measurement
system in a land-based operation.
DETAILED DESCRIPTION
[0026] The present disclosure relates generally to a system and
method for using fiber optics in a DAS system in a subsea
operation. Subsea operations may present optical challenges which
may relate to the quality of the overall signal in the DAS system
with a longer fiber optical cable. The overall signal may be
critical since the end of the fiber contains the interval of
interest, i.e., the well and reservoir sections. To prevent a drop
in signal-to-noise (SNR) and signal quality, the DAS system
described below may increase the returned signal strength with
given pulse power, decrease the noise floor of the receiving optics
to detect weaker power pulses, maintain the pulse power as high as
possible as it propagates down the fiber, increase the number of
light pulses that can be launched into the fiber per second, and/or
increase the maximum pulse power that can be used for given fiber
length.
[0027] FIG. 1 illustrates an example of a well system 100 that may
employ the principles of the present disclosure. More particularly,
well system 100 may include a floating vessel 102 centered over a
subterranean hydrocarbon bearing formation 104 located below a sea
floor 106. As illustrated, floating vessel 102 is depicted as an
offshore, semi-submersible oil and gas drilling platform, but could
alternatively include any other type of floating vessel such as,
but not limited to, a drill ship, a pipe-laying ship, a tension-leg
platforms (TLPs), a "spar" platform, a production platform, a
floating production, storage, and offloading (FPSO) vessel, and/or
the like. Additionally, the methods and systems described below may
also be utilized on land-based drilling operations. A subsea
conduit or riser 108 extends from a deck 110 of floating vessel 102
to a wellhead installation 112 that may include one or more blowout
preventers 114. In examples, riser 108 may also be referred to as a
flexible riser, flowline, umbilical, and/or the like. Floating
vessel 102 has a hoisting apparatus 116 and a derrick 118 for
raising and lowering tubular lengths of drill pipe, such as a
tubular 120. In examples, tubular 120 may be a drill string,
casing, production pipe, and/or the like.
[0028] A wellbore 122 extends through the various earth strata
toward the subterranean hydrocarbon bearing formation 104 and
tubular 120 may be extended within wellbore 122. Even though FIG. 1
depicts a vertical wellbore 122, it should be understood by those
skilled in the art that the methods and systems described are
equally well suited for use in horizontal or deviated wellbores.
During drilling operations, the distal end of tubular 120, for
example a drill sting, may include a bottom hole assembly (BHA)
that includes a drill bit and a downhole drilling motor, also
referred to as a positive displacement motor ("PDM") or"mud motor."
During production operations, tubular 120 may include a DAS system.
The DAS system may be inclusive of an interrogator 124, umbilical
line 126, and downhole fiber 128. Without any limitation any
optical fiber utilized in interrogator 124, umbilical line 126, or
downhole fiber 128 may be an ultra-low loss transmission fiber that
has higher power handling capability before non-linearity. This is
captured in the optical budget, bit is also chosen to enable higher
gain from co-propagating Raman amplification. An ultra-low loss
transmission fiber does not include higher doping or embedded
reflective features along the length of the ultra-low transmission,
characteristics that may be found in current fiber optic cables.
These characteristics increase light scattering within fiber optic
cable. The more doping and embedded reflective features within the
fiber optic cable, the larger a Rayleigh scattering coefficient of
the fiber optic cable will be, and vice versa.
[0029] Downhole fiber 128 may be permanently deployed in a wellbore
via single- or dual-trip completion strings, behind casing, on
tubing, or in pumped down installations. In examples, downhole
fiber 128 may be temporarily deployed via coiled tubing, wireline,
slickline, or disposable cables. FIGS. 31A-31D illustrate examples
of different types of deployment of downhole fiber 128 in wellbore
122 (e.g., referring to FIG. 1). As illustrated in FIG. 31A,
wellbore 122 deployed in formation 104 may include surface casing
3100 in which production casing 3102 may be deployed. Additionally,
production tubing 3104 may be deployed within production casing
3102. In this example, downhole fiber 128 may be temporarily
deployed in a wireline system in which a bottom hole gauge 3108 is
connected to the distal end of downhole fiber 128. Further
illustrated, downhole fiber 128 may be coupled to a fiber
connection 3106. Without limitation, fiber connection 3106 may
attach downhole fiber 128 to umbilical line 126 (e.g., referring to
FIG. 1). Fiber connection 3106 may operate with an optical
feedthrough system (itself comprising a series of wet- and dry-mate
optical connectors) in the wellhead that optically couples downhole
fiber 128 from the tubing hanger, to umbilical line 126 on the
wellhead instrument panel. Umbilical line 126 may include an
optical flying lead, optical distribution system(s), umbilical
termination unit(s), and transmission fibers encapsulated in flying
leads, flow lines, rigid risers, flexible risers, and/or one or
more umbilical lines. This may allow for umbilical line 126 to
connect and disconnect from downhole fiber 128 while preserving
optical continuity between the umbilical line 126 and the downhole
fiber 128.
[0030] FIG. 31B illustrates an example of permanent deployment of
downhole fiber 128. As illustrated in wellbore 122 deployed in
formation 104 may include surface casing 3100 in which production
casing 3102 may be deployed. Additionally, production tubing 3104
may be deployed within production casing 3102. In examples,
downhole fiber 128 is attached to the outside of production tubing
3104 by one or more cross-coupling protectors 3110. Without
limitation, cross-coupling protectors 3110 may be evenly spaced and
may be disposed on every other joint of production tubing 3104.
Further illustrated, downhole fiber 128 may be coupled to fiber
connection 3106 at one end and bottom hole gauge 3108 at the
opposite end.
[0031] FIG. 31C illustrates an example of permanent deployment of
downhole fiber 128. As illustrated in wellbore 122 deployed in
formation 104 may include surface casing 3100 in which production
casing 3102 may be deployed. Additionally, production tubing 3104
may be deployed within production casing 3102. In examples,
downhole fiber 128 is attached to the outside of production casing
3102 by one or more cross-coupling protectors 3110. Without
limitation, cross-coupling protectors 3110 may be evenly spaced and
may be disposed on every other joint of production tubing 3104.
Further illustrated, downhole fiber 128 may be coupled to fiber
connection 3006 at one end and bottom hole gauge 3008 at the
opposite end.
[0032] FIG. 31D illustrates an example of coiled tubing operation
in which downhole fiber 128 may be deployed temporarily. As
illustrated in FIG. 31D, wellbore 122 deployed in formation 104 may
include surface casing 3100 in which production casing 3102 may be
deployed. Additionally, coiled tubing 3112 may be deployed within
production casing 3102. In this example, downhole fiber 128 may be
temporarily deployed in a coiled tubing system in which a bottom
hole gauge 3108 is connected to the distal end of downhole fiber.
Further illustrated, downhole fiber 128 may be attached to coiled
tubing 3112, which may move downhole fiber 128 through production
casing 3102. Further illustrated, downhole fiber 128 may be coupled
to fiber connection 3106 at one end and bottom hole gauge 3108 at
the opposite end. During operations, downhole fiber 128 may be used
to take measurements within wellbore 122, which may be transmitted
to the surface and/or interrogator 124 (e.g., referring to FIG. 1)
in the DAS system.
[0033] Additionally, within the DAS system, interrogator 124 may be
connected to an information handling system 130 through connection
132, which may be wired and/or wireless. It should be noted that
both information handling system 130 and interrogator 124 are
disposed on floating vessel 102. Both systems and methods of the
present disclosure may be implemented, at least in part, with
information handling system 130. Information handling system 130
may include any instrumentality or aggregate of instrumentalities
operable to compute, estimate, classify, process, transmit,
receive, retrieve, originate, switch, store, display, manifest,
detect, record, reproduce, handle, or utilize any form of
information, intelligence, or data for business, scientific,
control, or other purposes. For example, an information handling
system 130 may be a processing unit 134, a network storage device,
or any other suitable device and may vary in size, shape,
performance, functionality, and price. Information handling system
130 may include random access memory (RAM), one or more processing
resources such as a central processing unit (CPU) or hardware or
software control logic, ROM, and/or other types of nonvolatile
memory. Additional components of the information handling system
130 may include one or more disk drives, one or more network ports
for communication with external devices as well as an input device
136 (e.g., keyboard, mouse, etc.) and video display 138.
Information handling system 130 may also include one or more buses
operable to transmit communications between the various hardware
components.
[0034] Alternatively, systems and methods of the present disclosure
may be implemented, at least in par, with non-transitory
computer-readable media 140. Non-transitory computer-readable media
140 may include any instrumentality or aggregation of
instrumentalities that may retain data and/or instructions for a
period of time. Non-transitory computer-readable media 140 may
include, for example, storage media such as a direct access storage
device (e.g., a hard disk drive or floppy disk drive), a sequential
access storage device (e.g., a tape disk drive), compact disk,
CD-ROM, DVD, RAM, ROM, electrically erasable programmable read-only
memory (EEPROM), and/or flash memory; as well as communications
media such as wires, optical fibers, microwaves, radio waves, and
other electromagnetic and/or optical carriers; and/or any
combination of the foregoing.
[0035] Production operations in a subsea environment present
optical challenges for DAS. For example, a maximum pulse power that
may be used in DAS is approximately inversely proportional to fiber
length due to optical non-linearities in the fiber. Therefore, the
quality of the overall signal is poorer with a longer fiber than a
shorter fiber. This may impact any operation that may utilize the
DAS since the distal end of the fiber actually contains the
interval of interest (i.e., the reservoir) in which downhole fiber
128 may be deployed. The interval of interest may include wellbore
122 and formation 104. For pulsed DAS systems such as the one
exemplified in FIG. 2, an additional challenge is the drop-in
signal to noise ratio (SNR) associated with the decrease in the
number of light pulses that may be launched into the fiber per
second (pulse rate) when interrogating fibers with overall lengths
exceeding 10 km. As such, utilizing DAS in a subsea environment may
have to increase the returned signal strength with given pulse
power, increase the maximum pulse power that may be used for given
fiber optic cable length, maintain the pulse power as high as
possible as it propagates down the fiber optic cable length, and
increase the number of light pulses that may be launched into the
fiber optic cable per second.
[0036] FIG. 32 illustrates an example of a land-based well system
3200, which illustrates a coiled tubing operation. Without
limitation, while a coiled tubing operation is shown, a wireline
operation and/or the like may be utilized. As illustrated
interrogator 124 is attached to information handling system 130.
Further discussed below, lead lines may connect umbilical line 126
to interrogator 124. Umbilical line 126 may include a first fiber
optic cable 304 and a second fiber optic cable 308 which may be
individual lead lines. Without limitation, first fiber optic cable
304 and a second fiber optic cable 308 may attach to coiled tubing
3202 as umbilical line 126. Umbilical line 126 may traverse through
wellbore 122 attached to coiled tubing 3202. In examples, coiled
tubing 3202 may be spooled within hoist 3204. Hoist 3204 may be
used to raise and/or lower coiled tubing 3202 in wellbore 122.
Further illustrated in FIG. 20, umbilical line 126 may connect to
distal circulator 312, further discussed below. Distal circulator
312 may connect umbilical line 126 to downhole fiber 128.
[0037] FIG. 2 illustrates an example of DAS system 200. DAS system
200 may include information handling system 130 that is
communicatively coupled to interrogator 124. Without limitation,
DAS system 200 may include a single-pulse coherent Rayleigh
scattering system with a compensating interferometer. In examples,
DAS system 200 may be used for phase-based sensing of events in a
wellbore using measurements of coherent Rayleigh backscatter or may
interrogate a fiber optic line containing an array of partial
reflectors, for example, fiber Bragg gratings.
[0038] As illustrated in FIG. 2, interrogator 124 may include a
pulse generator 214 coupled to a first coupler 210 using an optical
fiber 212. Pulse generator 214 may be a laser, or a laser connected
to at least one amplitude modulator, or a laser connected to at
least one switching amplifier, i.e., semiconductor optical
amplifier (SOA). First coupler 210 may be a traditional fused type
fiber optic splitter, a circulator, a PLC fiber optic splitter, or
any other type of splitter known to those with ordinary skill in
the art. Pulse generator 214 may be coupled to optical gain
elements (not shown) to amplify pulses generated therefrom. Example
optical gain elements include, but are not limited to, Erbium Doped
Fiber Amplifiers (EDFAs) or Semiconductor Optical Amplifiers
(SOAs).
[0039] DAS system 200 may include an interferometer 202. Without
limitations, interferometer 202 may include a Mach-Zehnder
interferometer. For example, a Michelson interferometer or any
other type of interferometer 202 may also be used without departing
from the scope of the present disclosure. Interferometer 202 may
include a top interferometer arm 224, a bottom interferometer arm
222, and a gauge 223 positioned on bottom interferometer arm 222.
Interferometer 202 may be coupled to first coupler 210 through a
second coupler 208 and an optical fiber 232. Interferometer 202
further may be coupled to a photodetector assembly 220 of DAS
system 200 through a third coupler 234 opposite second coupler 208.
Second coupler 208 and third coupler 234 may be a traditional fused
type fiber optic splitter, a PLC fiber optic splitter, or any other
type of optical splitter known to those with ordinary skill in the
art. Photodetector assembly 220 may include associated optics and
signal processing electronics (not shown). Photodetector assembly
220 may be a semiconductor electronic device that uses the
photoelectric effect to convert light to electricity. Photodetector
assembly 220 may be an avalanche photodiode or a pin photodiode but
is not intended to be limited to such.
[0040] When operating DAS system 200, pulse generator 214 may
generate a first optical pulse 216 which is transmitted through
optical fiber 212 to first coupler 210. First coupler 210 may
direct first optical pulse 216 through a fiber optical cable 204.
It should be noted that fiber optical cable 204 may be included in
umbilical line 126 and/or downhole fiber 128 (e.g., FIG. 1). As
illustrated, fiber optical cable 204 may be coupled to first
coupler 210. As first optical pulse 216 travels through fiber
optical cable 204, imperfections in fiber optical cable 204 may
cause a portion of the light to be backscattered along fiber
optical cable 204 due to Rayleigh scattering. Scattered light
according to Rayleigh scattering is returned from every point along
fiber optical cable 204 along the length of fiber optical cable 204
and is shown as backscattered light 228 in FIG. 2. This backscatter
effect may be referred to as Rayleigh backscatter. Density
fluctuations in fiber optical cable 204 may give rise to energy
loss due to the scattered light, .alpha..sub.scat, with the
following coefficient:
.alpha. scat = 8 .times. .pi. 3 3 .times. .lamda. 4 .times. n 8
.times. p 2 .times. k .times. T f .times. .beta. ( 1 )
##EQU00001##
where n is the refraction index, p is the photoelastic coefficient
of fiber optical cable 204, k is the Boltzmann constant, and .beta.
is the isothermal compressibility. T.sub.f is a fictive
temperature, representing the temperature at which the density
fluctuations are "frozen" in the material. Fiber optical cable 204
may be terminated with a low reflection device (not shown). In
examples, the low reflection device (not shown) may be a fiber
coiled and tightly bent to violate Snell's law of total internal
reflection such that all the remaining energy is sent out of fiber
optical cable 204.
[0041] Backscattered light 228 may travel back through fiber
optical cable 204, until it reaches second coupler 208. First
coupler 210 may be coupled to second coupler 208 on one side by
optical fiber 232 such that backscattered light 228 may pass from
first coupler 210 to second coupler 208 through optical fiber 232.
Second coupler 208 may split backscattered light 228 based on the
number of interferometer arms so that one portion of any
backscattered light 228 passing through interferometer 202 travels
through top interferometer arm 224 and another portion travels
through bottom interferometer arm 222. Therefore, second coupler
208 may split the backscattered light from optical fiber 232 into a
first backscattered pulse and a second backscattered pulse. The
first backscattered pulse may be sent into top interferometer arm
224. The second backscattered pulse may be sent into bottom
interferometer arm 222. These two portions may be re-combined at
third coupler 234, after they have exited interferometer 202, to
form an interferometric signal.
[0042] Interferometer 202 may facilitate the generation of the
interferometric signal through the relative phase shift variations
between the light pulses in top interferometer arm 224 and bottom
interferometer arm 222. Specifically, gauge 223 may cause the
length of bottom interferometer arm 222 to be longer than the
length of top interferometer arm 224. With different lengths
between the two arms of interferometer 202, the interferometric
signal may include backscattered light from two positions along
fiber optical cable 204 such that a phase shift of backscattered
light between the two different points along fiber optical cable
204 may be identified in the interferometric signal. The distance
between those points L may be half the length of the gauge 223 in
the case of a Mach-Zehnder configuration, or equal to the gauge
length in a Michelson interferometer configuration.
[0043] While DAS system 200 is running, the interferometric signal
will typically vary over time. The variations in the
interferometric signal may identify strains in fiber optical cable
204 that may be caused, for example, by seismic energy. By using
the time of flight for first optical pulse 216, the location of the
strain along fiber optical cable 204 and the time at which it
occurred may be determined. If fiber optical cable 204 is
positioned within a wellbore, the locations of the strains in fiber
optical cable 204 may be correlated with depths in the formation in
order to associate the seismic energy with locations in the
formation and wellbore.
[0044] To facilitate the identification of strains in fiber optical
cable 204, the interferometric signal may reach photodetector
assembly 220, where it may be converted to an electrical signal.
The photodetector assembly may provide an electric signal
proportional to the square of the sum of the two electric fields
from the two arms of the interferometer. This signal is
proportional to:
P(t)=P1+P2+2* {square root over ((P1P2)cos(.PHI.1-.PHI.2))} (2)
where P.sub.n is the power incident to the photodetector from a
particular arm (1 or 2) and .PHI..sub.n is the phase of the light
from the particular arm of the interferometer. Photodetector
assembly 220 may transmit the electrical signal to information
handling system 130, which may process the electrical signal to
identify strains within fiber optical cable 204 and/or convey the
data to a display and/or store it in computer-readable media.
Photodetector assembly 220 and information handling system 130 may
be communicatively and/or mechanically coupled. Information
handling system 130 may also be communicatively or mechanically
coupled to pulse generator 214.
[0045] Modifications, additions, or omissions may be made to FIG. 2
without departing from the scope of the present disclosure. For
example, FIG. 2 shows a particular configuration of components of
DAS system 200. However, any suitable configurations of components
may be used. For example, pulse generator 214 may generate a
multitude of coherent light pulses, optical pulse 216, operating at
distinct frequencies that are launched into the sensing fiber
either simultaneously or in a staggered fashion. For example, the
photo detector assembly is expanded to feature a dedicated
photodetector assembly for each light pulse frequency. In examples,
a compensating interferometer may be placed in the launch path
(i.e., prior to traveling down fiber optical cable 204) of the
interrogating pulse to generate a pair of pulses that travel down
fiber optical cable 204. In examples, interferometer 202 may not be
necessary to interfere the backscattered light from pulses prior to
being sent to photo detector assembly. In one branch of the
compensation interferometer in the launch path of the interrogating
pulse, an extra length of fiber not present in the other branch (a
gauge length similar to that of gauge 223) may be used to delay one
of the pulses. To accommodate phase detection of backscattered
light using DAS system 200, one of the two branches may include an
optical frequency shifter (for example, an acousto-optic modulator)
to shift the optical frequency of one of the pulses, while the
other may include a gauge. This may allow using a single
photodetector receiving the backscatter light to determine the
relative phase of the backscatter light between two locations by
examining the heterodyne beat signal received from the mixing of
the light from different optical frequencies of the two
interrogation pulses.
[0046] In examples, DAS system 200 may generate interferometric
signals for analysis by the information handling system 130 without
the use of a physical interferometer. For instance, DAS system 200
may direct backscattered light to photodetector assembly 220
without first passing it through any interferometer, such as
interferometer 202. Alternatively, the backscattered light from the
interrogation pulse may be mixed with the light from the laser
originally providing the interrogation pulse. Thus, the light from
the laser, the interrogation pulse, and the backscattered signal
may all be collected by photodetector assembly 220 and then
analyzed by information handling system 130. The light from each of
these sources may be at the same optical frequency in a homodyne
phase demodulation system, or may be different optical frequencies
in a heterodyne phase demodulator. This method of mixing the
backscattered light with a local oscillator allows measuring the
phase of the backscattered light along the fiber relative to a
reference light source.
[0047] FIG. 3 illustrates an example of DAS system 200 system,
which may be utilized to overcome challenges presented by a subsea
environment. DAS system 200 may include interrogator 324, umbilical
line 126, and downhole fiber 128. As illustrated, interrogator 324
may include pulse generator 214 and photodetector assembly 220,
both of which may be communicatively coupled to information
handling system 130. Additionally, interferometers 202 may be
placed within interrogator 324 and operate and/or function as
described above. FIG. 3 illustrates an example of DAS system 200 in
which lead lines 300 may be used. As illustrated, an optical fiber
212 may attach pulse generator 214 to an output 302, which may be a
fiber optic connector. Umbilical line 126 may attach to output 302
with a first fiber optic cable 304. First fiber optic cable 304 may
traverse the length of umbilical line 126 to a remote circulator
306. Remote circulator 306 may connect first fiber optic cable 304
to second fiber optic cable 308. In examples, remote circulator 306
functions to steer light unidirectionally between one or more input
and outputs of remote circulator 30. Without limitation, remote
circulators 306 are three-port devices wherein light from a first
port is split internally into two independent polarization states
and wherein these two polarization states are made to propagate two
different paths inside remote circulator 306. These two independent
paths allow one or both independent light beams to be rotated in
polarization state via the Faraday effect in optical media
Polarization rotation of the light propagating through free space
optical elements within the circulator thus allows the total
optical power of the two independent beams to uniquely emerge
together with the same phase relationship from a second port of
remote circulator 306.
[0048] Conversely, if any light enters the second port of remote
circulator 300 in the reverse direction, the internal free space
optical elements within remote circulator 306 may operate
identically on the reverse direction light to split it into two
polarizations states. After appropriate rotation of polarization
states, these reverse in direction polarized light beams, are
recombined, as in the forward propagation case, and emerge uniquely
from a third port of remote circulator 306 with the same phase
relationship and optical power as they had before entering remote
circulator 306. Additionally, as discussed below, remote circulator
306 may act as a gateway, which may only allow chosen wavelengths
of light to pass through remote circulator 36 and pass to downhole
fiber 128. Second fiber optic cable 308 may attach umbilical line
126 to input 309. Input 309 may be a fiber optic connector which
may allow backscatter light to pass into interrogator 324 to
interferometer 202. Interferometer 202 may operate and function as
described above and further pass back scatter light to
photodetector assembly 220.
[0049] FIG. 4 illustrates another example of DAS system 400. As
illustrated, interrogator 424 may include one or more DAS
interrogator units 401, each emitting coherent light pulses at a
distinct optical wavelength, and a Raman Pump 402 connected to a
wavelength division multiplexer 404 (WDM) with fiber stretcher.
Without limitation, WDM 404 may include a multiplexer assembly that
multiplexes the light received from the one or more DAS
interrogator units 401 and a Raman Pump 402 onto a single optical
fiber and a demultiplexer assembly that separates the
multi-wavelength backscattered light into its individual frequency
components and redirects each single-wavelength backscattered light
stream back to the corresponding DAS interrogator unit 401. In an
example, WDM 404 may utilize an optical add-drop multiplexer to
enable multiplexing the light received from the one or more DAS
interrogator units 401 and a Raman Pump 402 and demultiplexing the
multi-wavelength backscattered light received from a single fiber
WDM 404 may also include circuitry to optically amplify the
multi-frequency light prior to launching it into the signal optical
fiber and/or optical circuitry to optically amplify the
multi-frequency backscattered light returning from the single
optical fiber, thereby compensating for optical losses introduced
during optical (de-)multiplexing Raman Pump 402 may be a
co-propagating optical pump based on stimulated Raman scattering,
to feed energy from a pump signal to a main pulse from one or more
DAS interrogator units 401 as the main pulse propagates down one or
more fiber optic cables. This may conservatively yield a 3 dB
improvement in SNR. As illustrated, Raman Pump 402 is located in
interrogator 424 for co-propagation. In another example. Raman Pump
402 may be located topside after one or more remote circulators 306
either in line with first fiber optic cable 304 (co-propagation
mode) and/or in line with second fiber optic cable 308
(counter-propagation). In another example, Raman Pump 402 is
murinized and located after distal circulator 312 configured either
for co-propagation or counter-propagation. In still another
example, the light emitted by the Raman Pump 402 is remotely
reflected by using a wavelength-selective filter beyond a remote
circulator in order to provide amplification in the return path
using a Raman Pump 402 in any of the topside configurations
outlined above.
[0050] Further illustrated in FIG. 4, WDM 404 with fiber stretcher
may attach proximal circulator 310 to umbilical line 126. Umbilical
line 126 may include one or more remote circulators 306, a first
fiber optic cable 304, and a second fiber optic cable 308. As
illustrated, a first fiber optic cable 304 and as second fiber
optic cable 308 may be separate and individual fiber optic cables
that may be attached at each end to one or more remote circulators
306. In examples, first fiber optic cable 304 and second fiber
optic cable 308 may be different lengths or the same length and
each may be an ultra-low loss transmission fiber that may have a
higher power handling capability before non-literarily. This may
enable a higher gain, co-propagation Raman amplification from
interrogator 124.
[0051] Deploying first fiber optic cable 304 and as second fiber
optic cable 308 from floating vessel 102 (e.g., referring to FIG.
1) to a subsea environment to a distal-end passive optical
circulator arrangement, enables downhole fiber 128, which is a
sensing fiber, to be below a remote circulator 306 (e.g.,
well-only) that may be at the distal end of DAS system 400. Higher
(2-3.times.) pulse repetition rates, and non-saturated (non-back
reflected) optical receivers may also be adjusted such that their
dynamic range is optimized for downhole fiber 128. This may
approximately yield a 3.5 dB improvement in SNR. Additionally,
downhole fiber 128 may be a sensing fiber that has higher Rayleigh
scattering coefficient (i.e., higher doping) which may be result in
a ten times improvement in backscatter, which may yield a 7-dB
improvement in SNR. In examples, remote circulators 306 may further
be categorized as a proximal circulator 310 and a distal circulator
312. Proximal circulator 310 is located closer to interrogator 424
and may be located on floating vessel 102 or within umbilical line
126. Distal circulator 312 may be further away from interrogator
424 than proximal circulator 310 and may be located in umbilical
line 126 or within wellbore 122 (e.g., referring to FIG. 1). As
discussed above, a configuration illustrated in FIG. 3 may not
utilize a proximal circulator 310 with lead lines 300.
[0052] FIG. 5 illustrates another example of distal circulator 312,
which may include two remote circulators 306. As illustrated, each
remote circulator 306 may function and operate to avoid overlap, at
interrogator 124, of backscattered light from two different pulses.
For example, during operations, light at a first wavelength may
travel from interrogator 124 down first fiber optic cable 304 to a
remote circulator 306. As the light passes through remote
circulator 306 the light may encounter a Fiber Bragg Grating 500.
In examples, Fiber Bragg Grating 500 may be referred to as a filter
mirror that may be a wavelength specific high reflectivity filter
mirror or filter reflector that may operate and function to
recirculate unused light back through the optical circuit for
"double-pass" co/counter propagation induced DAS signal gain at
1550 nm. In examples, this wavelength specific "Raman light" mirror
may be a dichroic thin film interference filter, Fiber Bragg
Grating 500, or any other suitable optical filter that passes only
the 1550 nm forward propagating DAS interrogation pulse light while
simultaneously reflecting most of the residual Raman Pump
light.
[0053] Without limitation, Fiber Bragg Grating 500 may be set-up,
fabricated, altered, and/or the like to allow only certain selected
wavelengths of light to pass. All other wavelengths may be
reflected back to the second remote circulator, which may send the
reflected wavelengths of light along second fiber optic cable 308
back to interrogator 124. This may allow Fiber Bragg Grating 500 to
split DAS system 200 (e.g., referring to FIG. 4) into two regions.
A first region may be identified as the devices and components
before Fiber Bragg Grating 500 and the second region may be
identified as downhole fiber 128 and any other devices after Fiber
Bragg Grating 500.
[0054] Splitting DAS system 200 (e.g., referring to FIG. 4) into
two separate regions may allow interrogator 124 (e.g., referring to
FIG. 1) to pump specifically for an identified region. For example,
the disclosed system of FIG. 4 may include one or more pumps, as
described above, placed in interrogator 124 or after proximal
circulator 310 at the topside either in line with first fiber optic
cable 304 or second fiber optic cable 308 that may emit a
wavelength of light that may travel only to a first region and be
reflected by Fiber Bragg Grating 500. A second pump may emit a
wavelength of light that may travel to the second region by passing
through Fiber Bragg Grating 500. Additionally, both the first pump
and second pump may transmit at the same time. Without limitation,
there may be any number of pumps and any number of Fiber Bragg
Gratings 500 which may be used to control what wavelength of light
travels through downhole fiber 128. FIG. 5 also illustrates Fiber
Bragg Gratings 500 operating in conjunction with any remote
circulator 306, whether it is a distal circulator 312 or a proximal
circulator 310. Additionally, as discussed below, Fiber Bragg
Gratings 500 may be attached at the distal end of downhole fiber
218. Other alterations to DAS system 200 (e.g., referring to FIG.
4) may be undertaken to improve the overall performance of DAS
system 200. For example, the lengths of first fiber optic cable 304
and second fiber optic cable 308 selected to increase pulse
repetition rate (expressed in terms of the time interval between
pulses t.sub.rep).
[0055] FIG. 6 illustrates an example of fiber optic cable 600 in
which no remote circulator 306 may be used. As illustrated, at
least a portion of fiber optic cable 600 is a sensor and the pulse
interval may be greater than the time for the pulse of light to
travel to the end of fiber optic cable 600 and its backscatter to
travel back to interrogator 124 (e.g., referring to FIG. 1). This
is so, since in DAS systems 200 at no point in time, backscatter
from more than one location along sensing fiber (i.e., downhole
fiber 128) may be received. Therefore, the pulse interval t.sub.rep
may be greater than twice the time light takes to travel "one-way"
down the fiber. Let t.sub.s be the "two-way" time for light to
travel to the end of fiber optic cable 600 and back, which may be
written as t.sub.rep>t.sub.s.
[0056] FIG. 7 illustrates an example of fiber optic cable 600 with
a remote circulator 306 using the configuration shown in FIG. 3.
When a remote circulator 306 is used, only the light traveling in
fiber optic cable 600 that is allowed to go beyond remote
circulator 306 and to downhole fiber 128 may be returned to
interrogator 124 (e.g., referring to FIG. 1), thus, the interval
between pulses is dictated only by the length of the sensing
portion, downhole fiber 128, of fiber optic cable 600. It should be
noted that all light must travel "to" and "from" the sensing
portion, downhole fiber 128, with respect to pulse timing, what
matters is the total length of fiber "to" and "from" remote
circulator 306. Therefore, first fiber optic cable 304 or second
fiber optic cable 308 may be longer than the other, as discussed
above.
[0057] FIG. 8 illustrates an example remote circulator arrangement
800 which may allow, as described above, configurations that use
more than one remote circulator 306 close together at the remote
location. Although remote circulator arrangement 800 may have any
number of remote circulators 306, remote circulator arrangement 800
may be illustrated as a single remote circulator 306.
[0058] FIG. 9 illustrates an example first fiber optic cable 304
and second fiber optic cable 308 attached to a remote circulator
306 at each end. As discussed above, each remote circulator may be
categorized as a proximal circulator 310 and a distal circulator
312. When using a proximal circulator 310 and a distal circulator
312, light from the fiber section before proximal circulator 310,
and light from the fiber section below the remote circulator 306
are detected, which is illustrated in FIGS. 10 and 11. There is a
gap 1000 between them of "no light" that depends on the total
length of fiber (summed) between proximal circulator 310 and a
distal circulator 312.
[0059] Referring back to FIG. 9, with t.sub.s1 the duration of the
light from fiber sensing section before proximal circulator 310,
t.sub.sep the "dead time" separating the two sections (and due to
the cumulative length of first fiber optic cable 304 and second
fiber optic cable 308 between proximal circulator 310 and a distal
circulator 312), and t.sub.s2 the duration of the light from the
sensing fiber, downhole fiber 128, beyond distal circulator 312,
the constraints on fiber lengths and pulse intervals may be
identified as:
(i)t.sub.rep<t.sub.sep (3)
(ii)(2t.sub.rep)>(t.sub.s1+t.sub.sep+t.sub.s2) (4)
Criterion (i) ensures that "pulse n" light from downhole fiber 128
does not appear while "pulse n+1" light from fiber before proximal
circulator 310 is being received at interrogator 124 (e.g.,
referring to FIG. 1). Criterion (ii) ensures that "pulse n" light
from downhole fiber 128 is fully received before "pule n+2" light
from fiber before proximal circulator 310 is being received at
interrogator 124 is received. It should be noted that the two
criteria given above only define the minimum and maximum t.sub.rep
for scenarios where two pulses are launched in the fiber before
backscattered light below the remote circulator 306 is received.
However, it should be appreciated that for those skilled in the art
these criteria maybe generalized to cases where n.di-elect
cons.{1,2,3, . . . } light pulses may be launched in the fiber
before backscattered light below the remote circulator 306 is
received.
[0060] The use of remote circulators 306 (e.g., referring to FIG.
3) may allow for DAS system 200 (e.g., referring to FIG. 3) to
increase the sampling frequency. FIG. 12 illustrates workflow 1200
for optimizing sampling frequency when using a remote circulator
306 in DAS system 200. Workflow 1200 may begin with block 1202,
which determines the overall fiber length in both directions. For
example, a 17 km of first fiber optic cable 304 (e.g., referring to
FIG. 3) and 17 km of second fiber optic cable 308 (e.g., referring
to FIG. 3) before distal circulator 312 (e.g., referring to FIG. 3)
and 8 km of sensing fiber, downhole fiber 128 (e.g., referring to
FIG. 3), after distal circulator 312, the overall fiber optic cable
length in both directions would be 50 km. Assuming a travel time of
the light of 5 ns/m, the following equation may be used to
calculate a first DAS sampling frequency f.sub.s
f s = 1 t s = 1 5 10 - 9 z ( 5 ) ##EQU00002##
where t.sub.s is the DAS sampling interval and z is the overall
two-way fiber length. Thus, for an overall two way fiber length of
50 km the first DAS sampling rate f.sub.s is 4 kHz. In block 1204
regions of the fiber optic cable are identified for which
backscatter is received. For example, this is done by calculating
the average optical backscattered energy for each sampling location
followed by a simple thresholding scheme. The result of this step
is shown in FIG. 10A where boundaries 1002 identify two sensing
regions 1004. As illustrated in FIG. 10, optical energy is given
as:
I.sup.2+Q.sup.2 (6)
where I and Q correspond to the in-phase (I) and quadrature (Q)
components of the backscattered light. In block 1206, the sampling
frequency of DAS system 200 is optimized. To optimize the sampling
frequency a minimum time interval is found that is between the
emission of light pulses such that at no point in time
backscattered light arrives back at interrogator 124 (e.g.,
referring to FIG. 1) that corresponds to more than one spatial
location along a sensing portion of the fiber-optic line.
Mathematically, this may be defined as follows. Let S be the set of
all spatial sample locations x along the fiber for which
backscattered light is received. The desired light pulse emission
interval t.sub.s is the smallest one for which the cardinality of
the two sets S and {mod(x, t.sub.s):x.di-elect cons.S} is still
identical, which is expressed as:
min t s .times. ( t s ) .times. .times. s . t . .times. S = { mod
.times. .times. ( x , t s ) .times. : .times. .times. x .di-elect
cons. S } ( 7 ) ##EQU00003##
where | | is the cardinality operator, measuring the number of
elements in a set. FIG. 11 shows the result of optimizing the
sampling frequency from FIG. 10 with workflow 1200. Here, the DAS
sampling frequency may increase from 4 kHz to 12.5 kHz without
causing any overlap in backscattered locations, effectively
increasing the signal to noise ratio of the underlying acoustic
data by more than 5 dB due to the increase in sampling
frequency.
[0061] Variants of DAS system 200 may also benefit from workflow
1200. For example, FIG. 13 illustrates DAS system 1300 in which
proximal circulator 310 is placed within interrogator 1324. This
system set up of DAS system 1300 may allow for system flexibility
on how to implement during measurement operations and the efficient
placement of Raman Pump 402 in another illustrated example of DAS
system 1400, referring to FIG. 14. As illustrated in FIGS. 13 and
14, first fiber optic cable 304 and second fiber optic cable 308
may connect interrogator 124 to umbilical line 126, which is
described in greater detail above in FIG. 3.
[0062] FIG. 14 illustrates another example of DAS system 1400
having an interrogator 1424 in which Raman Pump 402 is operated in
co-propagation mode and is attached to first fiber optic cable 304
after proximal circulator 310. For example, if the first sensing
region before proximal circulator 310 should not be affected by
Raman amplification. Moreover, Raman Pump 402, may also be attached
to second fiber optic cable 308 which may allow the Raman Pump 402
to be operated in counter-propagation mode. In examples, the Raman
Pump may also be attached to fiber 1401 between WDM 404 and
proximal circulator 310 in interrogator 1424.
[0063] FIG. 15 illustrates another example of DAS system 1500 in
which an optical amplifier assembly 1501 (i.e., an Erbium doped
fiber amplifier (EDFA)+Fabry-Perot filter) may be attached to
proximal circulator 310, which may also be identified as a proximal
locally pumped optical amplifier. In examples, a distal optical
amplifier assembly 1502 may also be attached at distal circulator
312 on first fiber optical cable 304 or second fiber optical cable
308 as an inline or "mid-span" amplifier. In examples, optical
amplifier assembly 1502 located in-line with fiber optical cable
304 and above distal circulator 312 may be used to boost the light
pulse before it is launched into the downhole fiber 128. Referring
to FIGS. 10B and 10C, the effect of using an optical amplifier
assembly 1501 in-line with a second fiber optic cable 308 prior to
proximal circulator 310 and/or using an distal optical amplifier
assembly 1502 located in line with second fiber optical cable 308
above distal circulator 312 may allow for selectively amplifying
the backscattered light originating from downhole fiber 128 which
tends to suffer from much stronger attenuation as it travels back
along downhole fiber 128 and second fiber optical cable 308 than
backscattered light originating from shallower sections of fiber
optic cable that may also perform sensing functions. FIG. 10B
illustrates measurements where proximal circulator 310 is active
(optical amplifier assembly 1501 in-line with a second fiber optic
cable 308 prior to proximal circulator 310 and/or distal optical
amplifier assembly 1502 located in line with second fiber optical
cable 308 above distal circulator 312 is used). FIG. 10C
illustrates measurements where proximal circulator 310 is passive
(no optical amplification is used in-line with second fiber optic
cable 308). In FIGS. 10B and 10C, boundaries 1002 identify two
sensing regions 1004. Additionally, in FIGS. 10B and 10C the DAS
sampling frequency is set to 12.5 kHz using workflow 1200. Further
illustrated Fiber Bragg Grating 500 may also be disposed on first
fiber optical cable 304 between distal optical amplifier assembly
1502 and distal circulator 312.
[0064] FIG. 16 illustrates another example of DAS system 1600 in
which proximal circulator 310 and distal circulator 312 are
disposed within interrogator 1624. Without limitation, proximal
circulator 310 and distal circulator 312 may be disposed outside of
interrogator 1624 as a separate device but position on but may
still be disposed on floating vessel 102 (e.g., referring to FIG.
1) and/or above the water or earth surface. Similar to FIG. 4
above, interrogator 1624 may include one or more DAS interrogator
units 401, a Raman Pump 402, and a WDM 404 all of which may operate
and function according to the description above. As described
above, interrogator 1624 is attached to umbilical line 126, which
is attached to downhole fiber 128. Additionally, first fiber optic
cable 304 and second fiber optic cable 308 may connect proximal
circulator 310 and distal circulator 312. As illustrated in FIG.
16, second fiber optic cable 308 may be connected to an optical
shutter 1601 which protects an erbium-doped fiber amplifier (EDFA)
1602. The output from EDFA 1602 may connect second fiber optic
cable 308 to proximal circulator 310. This example may allow for
selective amplification, which may allow for the separation of the
optical path into a discrete down and up going paths. The up going
path being second fiber optic cable 308 and the down going path
being first fiber optic cable 304. In examples optical shutter 1601
is closed a down going pulse of light traverses through distal
circulator 312 and may remain close until such time that a
backscattered light from downhole fiber 128 approaches optical
shutter 1601 in second fiber optic cable 308. This may allow for
selective amplification of light from downhole fiber 128 and may
prevent all backscattered light, unless specifically chosen, from
reaching EDFA 1602.
[0065] FIG. 17 illustrates another example DAS system 1700 in which
optical shutter 1601 is disposed in interrogator 1724 and between
distal circulator 312 and umbilical line 126. Additionally, EDFA
1602 is disposed on second fiber optic cable 308 between proximal
circulator 310 and distal circulator 312. Optical shutter 1601 and
EDFA 1602 may still operate and function as described above in FIG.
16.
[0066] FIG. 18 illustrates another example DAS system 1800 in
which, as illustrated in FIG. 16, optical shutter 1601 and EDFA
1602 are disposed between proximal circulator 310 and distal
circulator 312 on second fiber optic cable 308. In addition, Raman
Pump 402 may be attached to WDM pump 1801 which is disposed on
first fiber optic cable 304. Raman Pump 402 and WDM pump 1801 may
operate and function as described in FIG. 14 above.
[0067] FIG. 19 illustrates an example including an optical
amplifier 1900. Optical amplifier 1900 may function and operate by
stimulated optical emission within a semiconductor optical
amplifier (SOA) using a material such as InGsAsP or by stimulated
emission of excited erbium ions within an Erbium doped fiber
amplifier (EDFA) or via non-linear optical energy conversion using
stimulated Raman processes, whereby optical energy is added to the
signal light in the optical domain. Optical amplifiers may be
pumped or excited via direct electron injection in the case of the
SOA or by local optical pumping, via laser diode, or remote
all-optical pumping of an EDFA or Distributed Raman Amplification
along the fiber itself. In example, optical amplifier 1900 is
disposed in umbilical line 126. Umbilical line 126 is attached to
interrogator 124 at one end and downhole fiber 128 at the opposite
end. As illustrated, optical amplifier 1900 may be attached to
shortwave optical Pump laser 402 at 1480 nm by pump laser fiber
1902, which may also be disposed in umbilical line 126. As
illustrated optical Pump laser 402 may operate and function to
excite the optical gain medium within the optical amplifier 1900 by
providing additional optical energy into the amplifier gain
medium.
[0068] FIG. 20 illustrates an example of two optical amplifiers
1900 disposed in umbilical line 126. In examples, each optical
amplifier 1900 may be disposed in series or in parallel with each
other. As illustrated, optical amplifiers 1900 are disposed in
series, which may allow for reduction in non-linear amplification
at each stage whereby the effective signal gain is provided via
summing of multiple gain stages. As illustrated, each optical
amplifier 1900 may be powered by a Raman Pump 402 connected by an
individual pump laser fiber 1902. In additional examples, a single
Raman Pump 402 may be connected to each optical amplifier 1900 by a
single pump laser fiber 1902 or two pump laser fibers 1902.
[0069] FIG. 21 illustrates another example in which optical
amplifier 1900 is disposed in umbilical line 126 and a proximal
circulator 310 and a distal circulator 312 are disposed between
interrogator 2124 and umbilical liner 126 on surface 2100. Surface
2100 is defined as on vessel 102 (e.g., referring to FIG. 1) or in
any suitable place above a body of water. As discussed above in
FIGS. 16-18, distal circulator 312 and proximal circulator 310 may
be connected by a first fiber optic cable 304 and a second fiber
optic cable 308. As illustrated, optical shutter 1601 and EDFA 1602
are disposed between proximal circulator 310 and distal circulator
312 on second fiber optic cable 308. In this example, optical
shutter 1600, EDFA 1602, and optical amplifier 1900 operate and
function as described above.
[0070] FIG. 22 illustrates an example DAS system 2200 that includes
two optical amplifiers 1900 disposed in umbilical line 126 with
proximal circulator 310 and distal circulator 312. In examples
distal circulator 312 and proximal circulator 310 may be connected
by a first fiber optic cable 304 and a second fiber optic cable
308. As illustrated, an optical amplifier 1900 is disposed in first
fiber optic cable 304 and second fiber optic cable 308. As noted
above, each optical amplifier 1900 is powered by an optical Pump
laser 402 that is connected to optical amplifier 1900 by a pump
laser fiber 1902. In this example, optical amplifiers 1900 may
operate and function to provide quasi distributed signal gain at
multiple locations along said fiber. FIG. 23 illustrates the same
setup as FIG. 22 but in this example DAS system 2300 each optical
amplifier 1900 is connected to a single pump laser fiber 1902,
which is connected to a single Raman Pump 402. FIG. 24 illustrates
another example DAS system 2400 with the same setup as FIG. 23,
however in this example proximal circulator 310 (e.g., referring
got FIG. 23) has been removed, leaving distal circulator 312. In
this example, the removal of proximal circulator 310 may allow for
both forward and return amplification with the proximal circulator
replaced with a second return fiber 2401.
[0071] FIG. 25 illustrates an example DAS system 2500 that an
optical amplifier 1900 disposed in umbilical line 126 with proximal
circulator 310 and distal circulator 312. As discussed above,
optical amplifier 1900 is connected to the optical Pump laser 402
by pump laser fiber 1902. In examples distal circulator 312 and
proximal circulator 310 may be connected by a first fiber optic
cable 304 and a second fiber optic cable 308. As illustrated, an
optical amplifier 1900 is disposed in first fiber optic cable 304.
In this example, optical amplifier 1900 may operate and function as
a single stage remotely-pumped EDFA or other lumped optical
amplifier along the outgoing transmission fiber. Remote pumping of
lumped in-line amplifiers allows tailoring of signal strengths for
optimum signal-to-noise ratios. FIG. 26 illustrates another example
DAS system 2600, with a similar setup of FIG. 25 with optical
amplifier 1900 disposed in second fiber optic cable 308 and not in
first fiber optic cable 304. As discussed above, optical amplifier
1900 is connected to Raman Pump 402 by pump laser fiber 1902. In
this example, optical amplifier 1900 may operate and function as a
single stage remotely-pumped EDFA or other lumped optical amplifier
along the returning transmission fiber. Remote pumping of lumped
in-line amplifiers allows tailoring of signal strengths for optimum
signal-to-noise ratios.
[0072] FIG. 27 illustrates an example schematic view of
interrogator 2724. As illustrated interrogator 2724 may be
connected to umbilical line 126 and downhole fiber 128 to form DAS
system 2700. As illustrated, umbilical line 126 may include any
number of distal circulators 312 and downhole fiber 128 may include
an optional Raman Mirror, which may also be referred to as Fiber
Bragg Grating 500.
[0073] Interrogator 2724 may include one or more lasers 2701.
Lasers 2701 may be multiplexing laser, which may operate by
multiplexing a plurality coherent laser sources via a WDM 404. One
or more lasers 2701 may emit a light pulse 2702, which may be of a
modified pulse shape. Optical pulse shaping and pre-distortion
methods may be employed to increase overall optical power that may
be launched into a fiber string 2704, which may connect one or more
lasers 2701 to proximal circulator 310. Light pulse 2702 may travel
from proximal circulator 310 through first fiber optic cable 304 to
WDM 404, which may be attached to a Raman Pump 402 at the opposite
end, and to umbilical line 126. Light pulse 2702 may travel to
distal circulator 312 in umbilical line 126 and the length of
downhole fiber 128. Any residual Raman amplification may be
reflected back by Fiber Bragg Grating 500 that has been constructed
to reflect the particular wavelengths used by the Raman Pump and
transmit all others. The backscattered light from the downhole
fiber 128 may travel back to distal circulator 312 and then up
second fiber optic cable 308 to a dedicated interrogator receiver
arm.
[0074] In examples, the dedicated interrogator receiver arm may
allow interrogator 2724 to selectively receive backscattered light
from different portions along the length of a fiber optic cable, as
seen in FIGS. 10 and 11. For example, interrogator receiver arm may
include a dedicated amplifier 2708 that may selectively amplify the
backscattered light from downhole fiber 128, a second region of the
fiber optic cable, using a higher amplification factor than the
dedicated amplifier 2708 used to selective amplify the
backscattered light received from first fiber optic cable 304, a
first region of the fiber optic cable. Gauges 2712 may have gauge
lengths employed in the two dedicated interrogator receiver arms
may differ (e.g., also described in FIG. 2). Finally, each
dedicated interrogator receiver arm may be equipped with receivers
2706 that are optimized according to certain characteristics of the
interferometric signals corresponding to the backscattered light
received from the two fiber sensing regions. Note that although
FIG. 27 only shows two dedicated interrogator receiver arms for
each sensing fiber regions, it is not intended to be limited to
such and may be extended to an arbitrary number of dedicated
interrogator receiver arms, where each receiver arm receives and
processes the backscattered light signal of a single sensing fiber
region of downhole fiber 128.
[0075] FIG. 27 further illustrates example inputs 2710 for
piezoelectric (PZT) devices. In examples, PZT devices functionally
allow dynamic stretching (straining) of optical fibers, which may
be embodied in coiled form around the PZT, attached thereto,
resulting in optical phase modulation of light propagating along
the attached optical fiber. The PZT elements are excitable via
electrical signals from any electronic signal information
generating source thus allowing information to be converted from
electrical signals to optical phase modulated signals along the
optical fiber attached thereto. Without limitation, PZT devices
attached to input 2710 may be a GPS receiver, seismic controller,
hydrophone, and/or the like.
[0076] FIG. 28 illustrates an example of a schematic view of
another example of interrogator 2824 with a single photon detector
(SPD) 2800. SPD 2800 replaces receivers 2706 (e.g., referring to
FIG. 27) within interrogator 2824. This allows for the removal of
Raman Pump 402, dedicated amplifier 2708, and WDM 404 (e.g.,
referring to FIG. 27) from interrogator 2824. Utilization of SPD
2800 alters DAS system 2700 (e.g., referring to FIG. 27) by
reducing the noise floor with DAS system 200 to increase SNR. The
noise floor is the average energy over a spectral range generated
by background processes in the detection system. For an optical
device, these may include thermal noise (due to fluctuations caused
by heat), pink noise (due to fluctuations caused by changing
defects), burst noise (due to fluctuations caused by static
defects), and shot noise (due to intrinsic fluctuations of the
electromagnetic field with the detector). An SPD 2800 may eliminate
(through reduction or compensation) all sources of noise except
shot noise and may lead to a reduction in the noise floor by up to
100 dB, directly increasing SNR.
[0077] In examples, SPD 2800 may be used in subsea operation or
land operations utilizing Rayleigh DAS, Raman Distributed
Temperature Sensing (DTS), and Brillouin Distributed Strain Sensing
(DSS). DTS operates and functions when a light pulse generates
backscattered signals due to inelastic scattering within optical
fiber. This inelastic scattering, which is strongly temperature
dependent, results in a frequency shift to lower frequency (Stokes
Raman Scattering) or higher frequency (Anti-Stokes Raman
Scattering), both of which are temperature dependent (and usually
around .about.13 THz). By detecting these two shifted
back-scattered signals, and appropriate math, the temperature may
be determined. DSS operates and functions on a photon inelastically
interacting with an acoustic phonon in an optical fiber. During the
interaction, momentum is transferred with the phonon and the
backscattered photon is frequency shifted (.about.9-11 GHz)
compared to the incident light frequency. The extent of frequency
shift is dependent on the strain and the temperature of the
fiber.
[0078] SPD 2800 may be cyro-cooled and operate and function
utilizing superconducting nanowire technology. In examples SPD 2800
does not require boosting of optical power but rather lowers the
noise floor of signal detection by up to a factor of 100 dB. The
detector in SPD 1700 may be designed to multiplex multiple
wavelengths or polarizations into the same detector system and may
have very narrow wavelength selectivity or larger optical
linewidths. These allow both strong wavelength selectivity without
the need of optical filters or enables detection of multiple
backscatter pulse types (Raman, Brillouin, Rayleigh) on the same
detector system. An SPD 2800 may include superconducting nanowire
single-photon detector, Photomultiplier tubes, Avalanche
photodiodes, Frequency up-conversion, Visible light photon counter,
Transition edge sensor, Quantum dots, and Perovskite/Graphene
phototransistors (for room temperature operation). In examples,
Multiple SPDs and beam-splitters may be used, such as in a homodyne
configuration comparing the sum and differences of two SPD signals
after a beam path is split by the beamsplitter), to determine the
extent of the contribution of shot noise of the overall signal. In
examples, the quantum efficiency of SPDs may range from .about.20%
up to 99.99%
[0079] FIG. 29 illustrates an example of a schematic drawing of SPD
2800. As illustrated, SPD 2800 may include a housing 2900 for
enclosing the optical detector 2902 and for providing an optical
shield for optical detector 2902. Housing 2900 may include an
aperture 2904 for passage of the fiber optic cable, which is
identified as second fiber optic cable 308. However, examples are
not limited thereto, and in some examples, a coupler may be mounted
so that second fiber optic cable 308 terminates at a boundary of
the housing 2900.
[0080] In examples, SPD 2800 may include a cooling mechanism 2906
having the housing 2900 mounted thereto. Cooling mechanism 2906 is
configured to maintain the temperature of a light-sensitive region
of optical detector 2902 within a temperature range below 210
degrees Kelvin. In some examples, cooling mechanism 2906 operates
using liquid helium (He) or liquid nitrogen (N2). In some examples,
cooling mechanism 2906 maintains the temperature of the
light-sensitive region of optical detector 2902 at a temperature at
or below 80 degrees Kelvin. In some examples, cooling mechanism
2906 maintains the temperature of the light-sensitive region of the
optical detector 2902 at a temperature at or below 5 degrees Kelvin
(e.g., when sealed helium systems are used). In some examples,
cooling mechanism 2906 may be of one or more of a variety of
configurations, including Dilutio-Magnetic, Collins-Helium
Liquefier, Joule-Thomson, Stirling-cycle cryocooler, self-regulated
Joule-Thomson, Closed-Cycle Split-Type Stirling, Pulse Tube, a
two-stage Gifford-McMahon cryogenic cooler or multi-stage
Gifford-McMahon cryogenic cooler, or a cooler using magnetocaloric
effect, by way of example. Lowering the temperature of optical
detector 2902 improves the SNR of optical detector 2902 by
decreasing dark current, by increasing sensitivity, and by reducing
resistive loss by causing optical detector 2902 to enter a
superconducting regime of operation. In some embodiments or
configurations non-SPD optical detectors 2902 may not enter a
superconducting regime, while still having little to no thermal
noise.
[0081] In some examples, SPD 2800 includes a cold head 2908 between
the optical detector 2902 and cooling mechanism 2906. However, some
embodiments do not include cold head 2908. In examples, housing
2900 is mounted to cooling mechanism 2906 such that moisture is
prevented from entering the housing. For example, housing 2900 may
be mounted such that a vacuum seal is formed with the cooling
mechanism 2906 or the cold head 2908. Additionally, housing 2900
may have a non-reflective inner surface.
[0082] As further illustrated in FIG. 29, SPD 2800 may further
include a switching or splitting mechanism 2910 to direct optical
signals to optical detector 2902, or a non-SPD optical detector
2912. Splitting mechanism 2910 may split optical signals based at
least in part on wavelength of the optical signal, power of the
optical signal, polarization, or any other parameter or criterion.
For example, high-power optical signals may be routed to non-SPD
optical detector 2912, and away from optical detector 2902 and
low-powered optical signals may be routed to optical detectors
2902. This routing may be performed to prevent damage to optical
detector 2902 while still taking full advantage of LLD and ELLD
capabilities of optical detector 2902. Without limitation,
high-power optical signals may cause saturation in optical detector
2902, leading to damage to optical detector 2902 or to inaccurate
results. In some examples, saturation of optical detector 2902 may
occur with optical signal inputs having a power of about 100
microwatts, and damage may occur at about 10 milliwatts. The noise
floor that may be detected by optical detector 2902 may be at a
level slightly below saturation level but is typically at least
20-30 dB. The saturation level and noise floors for non-SPD optical
detectors 2912 may be different from the saturation level and noise
floors for optical detector 2902. The saturation levels and noise
floors also may or may not overlap, and thus multiple types of
detectors may be used that may cover the full power range for
system measurements. For at least these reasons, to measure a
larger range of possible optical signals, optical detector 2902 are
used in a system with non-SPD optical detectors 2912. Splitting
mechanisms 2910 may direct or reroute optical signals based on
power level or other criteria, to take advantage of the different
power ranges measurable by optical detector 2902 versus non-SPD
optical detectors 2912.
[0083] In addition to or instead of a splitting mechanism 2910, SPD
2800 may include a coupling mechanism or other mechanism to split
the light with optical couplers (with or without feedback). These
mechanisms may be multi-stage (e.g., the light may be split in one
stage, then split again in a second stage), and may split light
based on power, wavelength, or phase. Processor or
computation-based systems may also be used in some embodiments to
dynamically direct or reroute light signals among any available
optical path as power increases or based on any other criteria.
[0084] In examples, SPD 2800 may be connected to information
handling system 130 (e.g., referring to FIG. 1) through
interrogator 2824 to obtain measurement data. In some examples,
some portions of the interrogator 2824 may be positioned at a
surface of the Earth, while some portions to interrogator 2824 may
be placed downhole. When more than one optical detector 1802 is
used, for example, some of the optical detectors 2902 or 2912 may
be placed downhole, and some may be placed at the surface. In some
examples, one or more cooling mechanisms 2906 may be placed
downhole proximate one or more optical detectors 2902 although
power and geometry considerations should be considered with such
configurations to provide power for cooling in an appropriately
sized borehole.
[0085] In production and/or measurement operations, the use of SPD
2800 may be safer than using a Raman Pump 402 (e.g., referring to
FIG. 27). Raman Pump 402 may increase the power moving through DAS
system 200, which may lead to explosions and damage from high power
increased by Raman Pump 402. Using SPD 2800 removes Raman Pump 402
and protects against explosions from hazardous gas used with Raman
Pump 402, increases eye safety by prevent high energy light pulses
from contacting the human eye, and may further prevent connector
damage and failure from high power densities. Additionally, as
lower optical pulse powers are used, non-linear distortion of the
optical pulse shape is negligible, allowing for minimal to no pulse
forming.
[0086] Utilizing SPD 2800 may improve current technology by
allowing greater lengths of fiber with greatly attenuated signals,
high transmission loss interconnects (such as used offshore) may be
used, even though the attenuation is high. An SPD 2800 may have
selective frequency, reducing background noise contribution of
other optical sources or devices (such as from a Raman pump or
scatter from a grating), and distortion of the optical pulse shape
is negligible. Additionally, an SPD 2800 may be gated extremely
fast, detect very few photons, and the spatial resolution can be
extremely high.
[0087] FIG. 30 illustrates another example DAS system 3000 having
an interrogator 3024 with optical shutter 1601 and EDFA 1602 are
disposed between proximal circulator 310 and distal circulator 312
on second fiber optic cable 308, as described in FIG. 16 above. In
addition, as described in FIG. 16, Raman Pump 402 may be attached
to WDM 1801 which is disposed on first fiber optic cable 304. Raman
Pump 402 and WDM 1801. In this example, distal circulator 312 is
disposed in umbilical line 126. In this example, interrogator 3024
may be configured to combine the optical pump laser for remote
amplification and signal laser from the interrogator onto one
common fiber.
[0088] The systems and methods for using a distributed acoustic
system in a subsea environment may include any of the various
features of the systems and methods disclosed herein, including one
or more of the following statements. Additionally, the systems and
methods for a DAS system within a subsea environment may include
any of the various features of the systems and methods disclosed
herein, including one or more of the following statements.
[0089] Statement 1. A distributed acoustic system (DAS) may
comprise an interrogator and an umbilical line attached at one end
to the interrogator, a downhole fiber attached to the umbilical
line at the end opposite the interrogator. The interrogator may
further include a proximal circulator, a distal circulator
connected to the proximal circulator by a first fiber optic cable,
and a second fiber optic cable connecting the proximal circulator
and the distal circulator.
[0090] Statement 2. The DAS of statement 1, further comprising an
erbium doped fiber amplifier (EDFA) disposed between the proximal
circulator and the distal circulator on the second fiber optic
cable.
[0091] Statement 3. The DAS of statement 2, further comprising an
optical shutter disposed between the EDFA and the distal circulator
on the second fiber optic cable.
[0092] Statement 4. The DAS of statement 3, further comprising a
wavelength division multiplexer (WDM) pump disposed on the first
fiber optic cable between the proximal circulator and the distal
circulator.
[0093] Statement 5. The DAS of statement 4, further comprising a
Raman Pump connected to the WDM pump.
[0094] Statement 6. The DAS of statement 2, further comprising an
optical shutter disposed between the distal circulator and the
umbilical line.
[0095] Statement 7. The DAS of statements 1 or 2, wherein the first
fiber optic cable and the second fiber optic cable are different
lengths.
[0096] Statement 8. The DAS of statements 1, 2, or 7, further
comprising at least one Fiber Bragg Grating attached to the
proximal circulator or the distal circulator.
[0097] Statement 9. The DAS of statements 1, 2, 7, or 8, wherein
the interrogator is configured to receive backscattered light from
a first sensing region and a second sensing region.
[0098] Statement 10. The DAS of statements 1, 2, or 7-9, wherein
the DAS is disposed in a subsea system operation of one or more
wells and the umbilical line attaches to the downhole fiber at a
fiber connection.
[0099] Statement 11. A distributed acoustic system (DAS) may
comprise an interrogator, an umbilical line attached to the
interrogator at one end, and a downhole fiber attached to the
umbilical line at the end opposite the interrogator.
[0100] Statement 12. The DAS of statement 11, further comprising an
optical amplifier disposed in the umbilical line that is connected
to a Raman Pump by a pump laser fiber.
[0101] Statement 13. The DAS of statements 11 or 12, further
comprising two optical amplifiers disposed in series in the
umbilical line that are each connected to individual Raman Pumps by
individual pump laser fibers.
[0102] Statement 14. The DAS of statement 13, wherein the two
optical amplifiers are connected to a Raman Pump by a pump laser
fiber.
[0103] Statement 15. The DAS of statements 11-14, further
comprising a proximal circulator, a distal circulator connected to
the proximal circulator by a first fiber optic cable, a second
fiber optic cable connecting the proximal circulator and the distal
circulator, and wherein the proximal circulator, the distal
circulator, the first fiber optic cable, and the second fiber optic
cable are disposed in the umbilical line.
[0104] Statement 16. The DAS of statement 15, further comprising a
first optical amplifier disposed on the first fiber optic cable
between the proximal circulator and the distal circulator.
[0105] Statement 17. The DAS of statement 16, further comprising a
second optical amplifier disposed on the second fiber optic cable
between the proximal circulator and the distal circulator.
[0106] Statement 18. The DAS of statement 17, wherein the first
optical amplifier is connected to a first Raman Pump by a first
pump laser fiber and the second optical amplifier is connected to a
second Raman Pump by a second pump laser fiber.
[0107] Statement 19. The DAS of statement 17, wherein the first
optical amplifier and the second optical amplifier is connected to
a Raman Pump by a pump laser fiber.
[0108] Statement 20. The DAS of statement 15, further comprising an
optical amplifier disposed on the second fiber optic cable between
the proximal circulator and the distal circulator.
[0109] Although the present disclosure and its advantages have been
described in detail, it should be understood that various changes,
substitutions and alterations may be made herein without departing
from the spirit and scope of the disclosure as defined by the
appended claims. The preceding description provides various
examples of the systems and methods of use disclosed herein which
may contain different method steps and alternative combinations of
components. It should be understood that, although individual
examples may be discussed herein, the present disclosure covers all
combinations of the disclosed examples, including, without
limitation, the different component combinations, method step
combinations, and properties of the system. It should be understood
that the compositions and methods are described in terms of
"comprising," "containing," or "including" various components or
steps, the compositions and methods can also "consist essentially
of" or "consist of" the various components and steps. Moreover, the
indefinite articles "a" or "an," as used in the claims, are defined
herein to mean one or more than one of the element that it
introduces.
[0110] For the sake of brevity, only certain ranges are explicitly
disclosed herein. However, ranges from any lower limit may be
combined with any upper limit to recite a range not explicitly
recited, as well as, ranges from any lower limit may be combined
with any other lower limit to recite a range not explicitly
recited, in the same way, ranges from any upper limit may be
combined with any other upper limit to recite a range not
explicitly recited. Additionally, whenever a numerical range with a
lower limit and an upper limit is disclosed, any number and any
included range falling within the range are specifically disclosed.
In particular, every range of values (of the form, "from about a to
about b," or, equivalently, "from approximately a to b," or,
equivalently, "from approximately a-b") disclosed herein is to be
understood to set forth every number and range encompassed within
the broader range of values even if not explicitly recited. Thus,
every point or individual value may serve as its own lower or upper
limit combined with any other point or individual value or any
other lower or upper limit, to recite a range not explicitly
recited.
[0111] Therefore, the present examples are well adapted to attain
the ends and advantages mentioned as well as those that are
inherent therein. The particular examples disclosed above are
illustrative only, and may be modified and practiced in different
but equivalent manners apparent to those skilled in the art having
the benefit of the teachings herein. Although individual examples
are discussed, the disclosure covers all combinations of all of the
examples. Furthermore, no limitations are intended to the details
of construction or design herein shown, other than as described in
the claims below. Also, the terms in the claims have their plain,
ordinary meaning unless otherwise explicitly and dearly defined by
the patentee. It is therefore evident that the particular
illustrative examples disclosed above may be altered or modified
and all such variations are considered within the scope and spirit
of those examples. If there is any conflict in the usages of a word
or term in this specification and one or more patent(s) or other
documents that may be incorporated herein by reference, the
definitions that are consistent with this specification should be
adopted.
* * * * *